Performance lighting systems have long employed large numbers of fixtures each selected and preadjusted to produce a beam of a particular size, shape, and color aimed at a fixed location on the stage. The only beam parameter variable during the performance is intensity, and the character of the lighting effect onstage is adjusted solely by changing the relative intensities of the variety of fixtures provided.
"Memory boards" allowing a user to store and subsequently recall "presets", each of which represents a digitally-coded record of the desired intensity for each of a plurality of discretely-controllable fixtures or groups of fixtures in a lighting effect have been known for decades, and the design of the modern, software-based, CRT-oriented memory board as disclosed in U.S. Pat. No. 3,898,643 has evolved to the point that such units are capable of--and lighting designers have come to demand--very complex effects. Further, lighting designers can choose from among various types and models of memory board differing in the manner in which they store cues (for example "tracking" versus "preset" boards) and in their operating protocols--and may have strong preferences for particular types and models as more familiar and/or more appropriate for a given production.
Despite the complexity of these dimming effects, lighting systems employing only fixtures controlling only intensity have the disadvantage of the need for many more fixtures than are used at any one time--or would be required were the fixtures capable of varying other beam parameters during the performance. There is the direct cost to buy or rent the large number of fixtures required plus their associated supporting structure, dimming equipment, and interconnecting cables as well as the time and labor required to install, adjust, and service this amount of equipment.
The electronic storage and recall of stored intensity values using "memory boards" has thus had no positive effect on the size of lighting systems, and indeed, by removing the practical limits on the number of control channels and presets which had been imposed by manual presetting consoles, the adoption of such electronic memory boards has lead to a substantial increase in the size of the lighting systems that employ them.
It has long been apparent that were fixtures able to change beam parameters in addition to intensity (like color, beam size, or even azimuth and elevation), either as the result of integral remotely actuatable mechanisms and/or devices (like color changers) which may be retrofitted to conventional fixtures, then lighting effects could be varied by actually changing the fixtures' beams rather than the dimming between otherwise identical fixtures with different fixed adjustments. Each such "multi-variable" fixture could, over the course of the performance, duplicate the results it currently requires many fixtures to achieve--as well as adding dynamic changes in the beam to the lighting effects possible --requiring fewer fixtures to produce a given lighting design with consequent savings.
The viability of employing fixtures with remotely adjustable beam size, color, shape and/or angle as a method of reducing system size depends upon a suitable control system, first disclosed in U.S. Pat. #3,845,351, capable of storing desired parameter values for each of the controlled parameters in each of the desired lighting effects and of automatically conforming the fixture's beam varying mechanisms to those values.
Similar systems were subsequently disclosed in U.S. Pat. #1,434,052 and U.S. Pat. #4,392,187, and today, the rental of such systems to concert, television, and theatrical productions is a multi-million dollar industry.
There have, however, been unexpected difficulties with developing a truly efficient embodiment of such a control system.
One class of such difficulties relate to the communications requirements between the centralized portion of the system and the variable parameter fixtures and devices controlled. Because a variable parameter fixture may provide for altering as many as eight different parameters of its beam, requiring the input of desired values for each, the total amount of data that must be transmitted over a serial data link between the centralized portion of a variable parameter control system and its fixtures or devices may total vastly more than that required in a conventional system controlling only intensity. One undesirable effect of this higher throughput has been very visible in at least one widely-used prior art automated lighting system. When the next "cue" in a sequence is executed, the changes in the beam parameters of the fixtures do not occur simultaneously, but "ripple" through the system, reflecting the time required to transmit new parameter values to each of the fixtures in the system.
Further, most conventional intensity control systems centralize the dimmers actually varying the fixtures' intensity in a limited number of racks or enclosures, limiting the number of nodes and therefore of decoders and connections on the serial data link. By contrast, variable parameter fixtures and devices mount the means varying each parameter on or in the fixture itself, requiring the distribution of multiplexed data to a very high number of nodes (and therefore decoders and connectors) distributed throughout the performance area, frequently in a far more EMI- and RFI-hostile environment than that encountered by a dimmer rack.
The use of automated lighting equipment therefore requires a data link that offers economy (given the number of decoders and interconnections required); greater reliability (given the more hostile environment); and far higher data rates (given the greater throughput required) than prior data links for intensity control.
Further, while prior disclosures of variable parameter systems were based on the assumption that such fixtures would be used on an exclusive basis, it has instead been the case that the number of variable parameter fixtures used per system may vary widely and that, contrary to expectations, variable parameter fixtures and devices of several different types may be employed in the same system, together with large numbers of conventional fixtures. These "read world" conditions further complicate the data transmission problem. To standardize on a data transmission scheme adapted for the demands of the largest possible number of the most sophisticated fixtures imposes a considerable penalty on system cost and complexity when used with smaller numbers of such fixtures and/or with fixtures and devices with more limited data requirements. Conversely, a data transmission scheme of more modest capability may be adequate to the needs of less demanding fixtures, but its decoders may be incapable of operation in a higher-performance system.
It is an object of the present invention to disclose techniques by which the communications workload on the data link between the centralized portion of a variable parameter control system and the fixtures and devices it controls may be reduced.